In general, when light strikes a surface, some of it may be reflected, some absorbed, some scattered, and the rest transmitted. Reflection can be diffuse, such as light reflecting off a rough surface such as a white wall, in all directions, or specular, as in light reflecting off a mirror at a definite angle. An opaque substance transmits almost no light, and therefore reflects, scatters, or absorbs all of it. Both mirrors and carbon black are opaque. Opacity depends on the frequency of the light being considered. “Blackout” or light blocking materials typically refer to coated layers in articles that are substantially impermeable to light such as visible or UV radiation. Thus, when a blackout material such as a blackout curtain or shade is hung over a window, it generally blocks substantially all external light from entering the room through that window. Blackout materials are suitable as curtains and shades for domestic use, for institutional use in hospitals and nursing homes, as well as for use in commercial establishments such as hotels, movie theaters, and aircraft windows where the option of excluding light can be desirable.
Light blocking articles such as the blackout curtains or shades can be comprised of a fabric (porous) substrate coated with more than one layer of a foamed latex composition. There is a desire for these curtains, in addition to blocking transmitted light, to have a light color (hue) facing the environment when an activity needs illumination so as to minimize the amount of artificial lighting needed to perform the activity. An example is when the function of the blackout material is to separate two areas of activity where one or both areas can be artificially lit at the same time. More often than not, the function of a blackout curtain is to prevent sunlight from entering a room through a building window. It can also be desirable for the color (hue) of the back side to match the external décor of the building.
Porous fabrics are derived from yarns of manmade or naturally-occurring threads that are woven or knitted together. Threads used to make yarn are often twisted together to form the threads. Synthetic plastic coating materials, such as polyvinyl chloride, led to the emergence of fabrics woven from plastic coated yarns. Such fabrics have increased durability and wear properties compared to fabrics made from naturally-occurring fibers. One use for such fabrics is window shades especially for commercial sites. Synthetic woven fabric consisting of bonded PVC-coated polyester and fiberglass yarns are described in U.S. Pat. No. 4,587,997 (Brooks). Fiberglass core yarns with plastic coatings can provide durability and dimensional stability.
Light colored blackout curtains can be made by coating porous fabrics with light colored foams containing light scattering pigments such as titanium dioxide or clays. However, very thick foam coatings will be needed to create blackout curtains through which the sun is not visible in a darkened room using only these pigments. One method that is used to reduce the weight of such blackout materials is to sandwich a light-absorbing, foamed black or grey pigment, such as carbon black layer between two light scattering, white pigment-containing layers.
When an electromagnetic radiation blocking coating has, as it often does, a strongly light absorbing material containing black pigments such as carbon black, between two reflective layers, it has at least two distinct problems. First, such materials require three separate coating operations that reduce manufacturing productivity and increase unit costs. Secondly, carbon black in the light absorbing middle layer can become “fugitive” (or non-enclosed) from some puncture or tear occurring during sewing or laundering, and soil other layers such as the reflective layers, which is highly objectionable. Additionally, the stitches generated in the materials during sewing can cause the fugitive carbon from the light absorbing layer to spread over a larger area thereby increasing the area of objectionable shading of the light-colored surface.
U.S. Pat. No. 7,754,409 (Nair et al.), U.S. Pat. No. 7,887,984 (Nair et al.), U.S. Pat. No. 8,252,414 (Putnam et al.), and U.S. Pat. No. 8,329,783 (Nair et al.) describe porous polymer particles that are made by a multiple emulsion process, wherein the multiple emulsion process provides formation of individual porous particles comprising a continuous polymer phase and multiple discrete internal pores, and such individual porous particles are dispersed in an external aqueous phase. The described Evaporative Limited Coalescence (ELC) process is used to control the particle size and distribution while a hydrocolloid is incorporated to stabilize the inner emulsion of the multiple emulsion that provides the template for generating the pores in the porous particles.
U.S. Patent Application Publication 2015/0234098 (Lofftus et al.) describes improved articles that are designed with an opacifying layer that is capable of blocking predetermined electromagnetic radiation. The opacifying layer is disposed on a substrate that can be composed of any suitable material and a porous or non-porous underlying layer can be incorporated between the substrate and the opacifying layer. While these articles have numerous advantages and represent an important advance in the art, there is a need for further improvement in providing opacifying articles that are lighter in weight; and that have improved flexibility, good “hand,” while maintaining light coloration of the surfaces facing an observer without losing reflectivity, and light-absorptive properties; launderability; and minimizing dark opacifying agents getting out into the environment upon stitching and handling.
An improvement in this art is provided by the foamed aqueous compositions described and claimed in recently allowed U.S. Ser. No. 15/144,875 (noted above) in which very small amounts of opacifying colorants can be incorporated into porous particles, and the resulting composition has a foam density of at least 0.1 g/cm3.
U.S. Pat. No. 4,677,016 (Ferziger) describes a foam-coated, tightly woven fiberglass fabric where at least one surface thereof is coated with one or more layers of a flame retardant foamed coating composition. At least one of the foam coating layers is opaque and comprises a cured layer of flame retardant polymeric latex foam. This foam coating is said to render the fabric substantially impermeable to light and is applied to the surface of the fiberglass substrate in an amount sufficient to make the fabric non-abrasive, abrasion resistant, easily sewn, and drapeable.
There is a continued need for improvements in the art described materials, especially for making light-blocking materials designed for use as window shades for maximum privacy derived from porous woven substrates comprising plastic coated multifilament core yarns.